In recent years, an organic light-emitting element, which is self-emissive with a low drive voltage of several volts, has attracted attention. An organic light-emitting element generally has a structure in which a reflective electrode having a metal reflecting layer, an emission layer, and a light extraction electrode are stacked. Such an organic light-emitting element has excellent characteristics such as surface emitting characteristics, light weight, and visibility, and due to its characteristics, is being commercialized as a light-emitting device for, for example, a thin display, a lighting apparatus, or a head-mounted display, or as a light source for a print head of an electrophotographic printer.
A demand for a higher definition organic electroluminescent (EL) display device has been particularly increasing, and a system using an organic white-light-emitting element and a color filter (hereinafter referred to as “white+CF system”) has been attracting attention (Non Patent Literature 1). The “white+CF system” enables solid vapor deposition of an organic film on an entire surface of a substrate without using an extra-fine metal mask, and thus, a higher yield can be expected compared with that of the system of discrete pixelation using a mask. Further, the use of a color filter enables reductions in a pixel size and an inter-pixel pitch to a limit of photolithography, to thereby comparatively easily attain a higher definition.
Further, in the “white+CF system”, a tandem element is often used from the viewpoint of durability, and a tandem element is also used in Non Patent Literature 1. A tandem element generally has a structure in which a plurality of organic EL units are stacked between a cathode and an anode via a charge generation layer. Therefore, the tandem element has excellent characteristics that a current per element can be reduced to reduce the rate of drive degradation.